The field of the invention is blood analysis by optics, measuring and testing and the invention is particularly related to a method and apparatus for determining a test value corresponding to blood subsidence from a syllectogram of a blood sample that is being subjected to shear forces.
The state of the art of determining a test value corresponding to blood subsidence from a syllectogram of a blood sample that was or is being subjected to shear forces may be ascertained by reference to the article entitled "Syllectometry" by Zijlstra, as published in the Proc. Koninkl. Nederl. Akad. v. Wetensch., Amsterdam, Ser. C., Vol. 66, no. 3 (1963) at pp. 237-248.; Microvascular Research, Vol. 6, (1973), pp. 366-376; and U.S. Pat. No. 4,135,819, of Schmid-Schonbein, the disclosures of which are incorporated herein.
U.S. Pat. No. 4,135,819 discloses an apparatus and method for measuring the aggregation rate of capillary native blood free of coagulation inhibitor in order to quickly ascertain information disclosing blood subsidence from a minimum amount of blood. In U.S. Pat. No. 4,135,819, the light transmission of a blood sample is recorded as a function of time. This magnitude changes as a function of the significant rheological phenomenon, the erythrocyte aggregation, and therefore permits data to be obtained. Photometric aggregometry may be measured both in transmission and reflection. The test curve obtained was first coined "syllectogram" by Zijlstra, op. cit. It is based on the fact that the scattering of light in a blood sample decreases after aggregates are formed and the transmission of light increases accordingly.
Three basic phases must be distinguished in the course of a measurement, namely: (1) the mixing phase, (2) the stopping phase, i.e., the phase of slight shearing, and (3) the aggregation phase. To carry out the measurement, a blood sample is introduced into a measuring chamber consisting essentially of a transparent, disk-cone system rotating in the same or mutually opposite directions. During the mixing phase, the erythrocytes orient themselves under the influence of shearing forces and thus create clear plasma spaces by means of which the light can pass through the blood sample. In view of the material inhomogeneities in the path of the light beam, the light transmission fluctuates about a mean value.
When the shearing is terminated by abruptly stopping the disk-cone system, there is an impulsive disorientation of the blood cells and as a consequence of the elimination of clear plasma spaces, there is also a reduction in the transmission.
With the ensuing onset of aggregation, the number of plasma gaps grows again and therefore the transmission increases again. The change of this transmission with time is essentially exponential.
This time curve is quite reproducible, so that first the half-value time characteristic of an exponential function was determined to be the numerical value. It has been found, however, that no unambiguous correlation could be obtained between this numerical value and the conventionally obtained blood subsidence values.
It is furthermore known from Microvascular Research, op. cit., that the syllectogram representing the time function of erythrocyte aggregation presents a significantly higher test value in the presence of a slight residual shearing than for the measurement at rest.
U.S. Pat. No. 4,135,819 proposed not to use the measured curve, but its derivative with time. This differentiated curve is also exponential, whereby the erythrocyte aggregation again can be represented by the half-value time of the differentiated syllectogram. The half-value time is plotted by hand, or for a rapid aggregation by electronic differentiation. But it has been found that while the analog differentiation is quite suitable for all pathological, i.e., rapid aggregation processes, it requires a high expenditure in material for the slow ones. This is especially the case for extremely decelerated aggregation which occurs in healthy blood after it is diluted by an anticoagulant dissolved therein.